Transmission regulation



, H.A.AFFEL TRANSMISSION REGULATION Filed May 4 922 l i 4 MIR, i

llllll slam I x .q 2 0 E0 3 2 INVEN A TITORNEY:

Patented Oct. 7, 1924.

UNITED STATES PATENT orr cs.

vHERMAN A. AFFEL'O'F BROOKLYN, NEW YORK, ASSIGNOR 'I'O AMERICANTELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

TRANSMISSION REGULATION.

Application filed May 4,

To all whom it may concern:

Be it known that I, HERMAN A. AFFEL residing at Brooklyn, in the countyof Kings and State of New York, have invented certain Improvements inTransmission Regulations, of which'the following is a specification.

This invention relates to multiplexsignaling circuits, and moreparticularly to methods and arrangements for controlling thetransmission over such circuits.

In a wire carrier or radio telephone system, the fluctuations inattenuation of the transmission medium or line produce correspondingvariations in the over-all\transmission equivalent of the voice circuit.In one well known type of carrier system, the carrier frequency itselfis suppressed at the modulator end in connection with each channel, andthe fundamental frequency, which is relatively low; is transmitted tothe receiving end of the circuit, and by harmonic regeneration, causedto produce a synchronous carrier supply for .the respectivedemodulators. The carrier supply in this case is transmitted at afrequency which is substantially independent of rdinary line attenuationfluctuations and the variation in line attenuation at the side bandfrequency causes a directly proportional variation in the over-allequivalent, there being substan- .tially no fluctuation of theequivalent of the circuit due to the carrier component itself. With thetype of carrier system, however,

' in which a carrier frequency is transmitted along with the side bandof each individual channel, the transmission fluctuations may be evenmore serious, since in demodulationthe resultant voice output may, fornormal operation of the demodulator, be proportional to the product ofthe carrier and the modulated side band. If,'therefore, the attenuationof the intervening line or other transmission medium varies,approximately the same variation will take place for" both the carrierand the modulated side band, and the resultant voice circuit variation,being proportional to the product of these two factors, will beapproximately double that of the line attenuation itself. 1"

In accordance with the present inventio it is proposed toovercome thedifficulti s encountered in connection with transmission fluctuations inthe type of circuit in which the'carrier frequency is transmitted 1922.Serial No. 558,446.

at a receiving station by selecting the cari rier frequency component,rectifying the-selected component to produce a direct current whoseamplitude will depend onfthe transmission conditions to which thecarrier has been subjected, and controlling the transmission element bythe rectified current.- Thecontrol exercised by the rectified currentmay be effected either electrically or mechanically, but in thepreferred form herein disclosed, an electrical system of controlillustrated. a

The invention may now be more fully understood by reference to thefollowing description, when read in connection with the accompanyingdrawing, Figure 1 of which shows a circuit diagram embodying theprinciples of the invention, and Fig. 2 is a curve illustrating theoperation of one of the vacuum itube circuits shown in Fig. 1.

Referring to Fig. 1, so much of the carrier systemiis shown as isnecessary to an understandin of the present invention. In this figure;TEL designates the receiving channel of one transmission circuit of acarrier telegraph system, said channel be ing connected, together withother similar channels (riot shown), to a common transmission line' (notshown), over which carrier frequenciesl are transmitted. Thecorresponding t 'ansmitting' channel is not illustrated, as it is notinvolved in the present invention. The receiving channel RL includes aband filter RF for selecting the desired side band and the correspondingcarrier,a detector D and a receiving amplifier RA. The detector D may beof any well known type,'such as a vacuum tube detector,

and is adapted to detect the voice currents corresponding to the sideband by beating the side band with the carrier.

as the unmodulated carrier component ap-' pea-ring in the output circuitof the detedtor. The output circuit of the receiving am- Thereceivplifier RA includes a transformer 11 by which the low frequencycircuit 13 (which may be associated with a low frequency transmissionline) is connected to the receiving channel.

The circuit 13 includes a low-pass filter by which the voice frequencycurrents are selected into said circuit to the exclusion of the higherfrequency components, such as the unmodulated carrier. The carrierfrequency component may be selected by means of a tuned circuit orfilter 12 through which the carrier frequency is impressed upon arectifier R. The rectifier R may be of any well known type but isillustrated as a vacuum tube arrangement adapted to translate theselected carrier component into a direct current. Insystems of thistype, this direct current is primarily used to control the operation ofa signal relay SR, which is illustrated as being included in the outputcircuit of the rectifier. This signal relay is adapted to operate aringing signal when the carrier is interrupted at the sending station,the interruption of the carrier (which is normally transmitted)resulting in the cessation of the flow of direct current in the outputcircuit of the rectifier.

In the present invention, this circuit is also utilized to control thetransmission efficiency of the detector D, and for this purpose theoutput circuit of the rectifier may be traced from ground to thefilament of the rectifier, through the space in the tube to the plate ofthe rectifier and then through the Winding of the relay SR, battery B topoint 14 of resistance 15, thence to junction point 16 of resistances 15and 17, through the resistance 17 and through the series connectedfilaments of the detector D, amplifier RA and rectifier R to ground. Aconnection also extends from the point 11, through the upper half .ofresistance 15 to the grid of the detector D. It will be seen, therefore,that the potential of the grid I) is made to depend upon the amplitudeof the rectified current flowing in the plate circuit of the rectifierR.

Disregarding for the moment the connection of this late circuit to thegrid of the detector D through the point 14, it will be seen that thegrid of the detector D may he made normally negative with respect to thefilament, by reason of the fact that the battery A, which supplies thefilament heating current through the resistance 17, is connected to thegrid of the detector D through the resistance 15, and by properlyproportioning the resistance 15 with respect to the resistance 17, thegrid may be made more negative than the filament. The connection of theplate circuit of the rectifier R to the point it, however, results insuperposing a negative potential (depending upon the value of therectified current) upon the grid of the detector D, in addition to thenegative potential supplied from the battery A. Under normaltransmission conditions, the rectified current flowing in the platecircuit of the rectifier R will have a definite negative potential, sothat the resultant potential upon the grid of the detector D may be madeto correspond to the point 3 of the characteristic curve a of Fig. 2,this curve representing the variation in the plate current of thedetector with variation in the grid potential of the detector.

The point a: of the characteristic curve may be taken as the point atwhich the greatest curvature occurs, and consequently, the detector willbe most efficient at this point. The point a of the characteristic curveis a point at which the curvature is much less than at the point a", andthis may be considered the point at which the detector Will be leasteflicient over its practical operating range. The point y is chosen atan intermediate point between the points a: and 2, so that under averagetransmission conditions, the detector will be working at the point y.Consequently, if the transmission efficiency of the carrier circuit ormedium is decreased," so that the amplitude of the carrier current isdecreased, the rectified direct current flowing in the output circuit ofthe rectifier R will be correspondingly decreased and the grid of thedetector will become more positive, so that the operating point of thedetector will be shifted toward the point 00, thereby increasing theefficiency of the detector This increased efficiency will obviouslymanifest itself not only in an increased detection efiiciency, but sincethe operation is now taking place on a portion of the characteristiccurve which has greater slope, itwill also manifest itself in greateramplification for the currents which pass through the tube substantiallyundistorted, such as the carrier current itself. By a proper adjustment,this increase in efficiency may be made to compensate for the decreasedamplitude of the carrier and side band, so that the resultant detectedvoice currents will be the same as under average conditions.

Likewise, if the efficiency of the transmission medium be increasedabove the average condition, the amplitude of the carrier current willbe increased, with a corresponding increase in the amplitude of thedirect current flowing in the output circuit of the rectifier R.Consequently, the grid of the detector D will be made more negative thanbefore, and its operating point will be shifted toward a with acorresponding decrease in the operating eificiency of the detector. Thisdecrease may be so regulated in any given case as to compensate for theincreased amplitude of the carrier and side band, with the result thatthe detected voice frequency will be substantially no greater than underthe average condition. It will be evident that the effectiveamplification of the detector will also be decreased because theoperation will take place over a portion of the characteristic curvewhich is less steep.

In this manner, the change in transmis sion conditions in the carriercircuit may be automatically compensated for electrically and this,compensation automatically takes place regardless of whether the circuitis being used for signaling purposes or not. In other words, the carriercurrent being transmitted at all times regardless of whether or notthere is an accompanying side band, and the control of the efiiciency ofthe detector depending upon the amplitude of the carrier frequency, theregulation of transmission will take place whether or not the side bandis transmitted. It will be obvious that the general principles hereindisclosed may be embodied in many other organizations widelydifferentfrom those illustrated, without departing from the spirit ofthe invention as defined in the following claims.

What is claimed is:

1. The method of controlling transmission in a carrier system in whichthe carrier .is transmitted along with the side band and in which adetector is employed to detect the signal, which consists intransmitting the carrier and side band over a medium whose transmissionis variable under different conditions, combining the carrier togetherwith the side band in the detector to detect the low frequency signalingwave represented by the side band, selecting the unmodulated carrierfrom the output current of the detector, producing from the selectedcarrier a current having characteristics depending upon the transmissionconditions to which the carrier has been subjected, and controlling theefiiciency of the detector in accordance with the character istics ofthe current thus produced to compensate for the change in efliciency ofthe transmitting medium.

2. The method of controlling transmission in a carrier system in whichthe carrier is transmitted along with the side band and in which adetector is employed to detect the signal, which consists intransmitting the carrier and side band over a medium whose transmissionis variable under different conditions, combining the carrier togetherwith the side band in the detector to detect the low frequency signalingwave represented by the side band, selecting the unmodulated carrierfrom the output current of the detector, producing from the selectedcarrier a direct current whose amplitude depends upon the transmissionconditions to which the carrier has been subjected, and controlling theefiiciency of the detector in accordance with the amplitude of thedirect current thusproduced to compensate for the change in efliciencyof the transmitting medium.

3. The method of controlling transmissionin a carrier system in whichthe carrier is transmitted along with the side band, which consists intransmitting the carrier and side band over a medium whose transmissionis variable under different conditions, combining the carrier and sideband in a receiving channel, selecting the carrier, producing from theselected carrier a current whose characteristics depend upon thetransmission conditions to which the carrier has been subjected, andcontrolling the electrical characteristics of a transmission element ofthe receiving channel by means of the current thus produced tocompensate for the change in'efiiciency of the transmitting medium.

4. The method of controlling transmission in a carrier system in whichthe carrier is transmitted along with the side band, which consists intransmitting the carrier and side band over a medium whose transmissionis variable under different conditions, combining the carrier and sideband in a receiving channel, selecting the carrier,

rectifying the selected carrier to produce a directcurrent whoseamplitude depends upon the transmission conditions to which the carrierhas been subjected, and controlling the electrical characteristics of acircuit element of the receiving channel by means of the rectifiedcarrier current to compensate for the change in efliciency of thetransmitting medium.

5. The method of controlling transmission in a carrier system in whichthe car rier is transmitted along with the side band and in which thereceiving channel includes a detector for detecting the signal, whichconsists in transmitting the carrier and side band over a medium whosetransmission is variable under different conditions, combining thecarrier and side band in the detector of the receiving channel,selecting the carrier, producing from the selected carrier at currentwhose characteristics depend upon the transmission conditions to Whichthe carrier has been subjected, and controlling the efliciency of thedetector in the receiving channel by means of the current thus producedto compensate for the change in efi'iciency of the transmitting medium.

6. The method of controlling transmission in a carrier system in whichthe carrier is transmitted along with the side band and in which thereceiving channel includes a detector, which consists in transmittingthe carrier and side band over a medium whose transmission is variableunder different conditions, combining the carrier and side band in thedetector of the receiving channel, selecting the carrier, rectifying theselected carrier to produce a direct current whose amplitude dependsupon the transmission conditions to which the carrier has beensubjected, and controlling the efficiency of the detector in thereceiving channel by means of the rectified carrier current tocompensate for the change in etiicicncy of the transmitting medium.

7. The method of controlling transmission in a carrier system in whichthe carrier is transmitted along with the side band and in'which thereceiving channel includes a detector for detecting the signal. whichconsists in transmitting the carrier and side band over a medium whosetransmission is variable under different conditions, combining thecarrier together with the side band in the detector to produce lowfrequency signaling currents represented by the side band, selecting theunmodulated carrier component from the output. current of the detector,producing from the selected carrier component a direct current whoseamplitude varies. in accordance with the transmission conditions towhich the carrier has been subjected, and controlling the efliciency ofthe detector in accordance with the amplitude of said direct current tocompensate for changes in the efliciency of the transmitting); medium.

8. The method of controlling transmission in a carrier system in whichthe carrier transmitted along with the side band and in which a vacuumtube detector haw ing a controlling grid is employed to detect thesignal. which consists in transmitting the carrier and side band over amedium whose transmission is variable under ditl'crcnt conditions,combining the carrier together with the side band in the detector toproduce low frequency signaling currents represented by the side band,selecting the umnodulated carrier component from the output current ofthe detector, rectifying the selected carrier component to produce adirect current whose amplitude varies in accordance with thetransmission conditions to which the carrier has been subjected, andcontrolling the normal potential of the grid of the detector by saiddirect current to change its operating characteristics to compensate forchanges in the efficiency of the transmitting medium.

9. In a system for controlling transmission, a transmitting medium overwhich the carrier is transmitted together with the side band, thetransmission efficiency of said medium being variable under differentconditions, a receiving channel including a detector upon which the sideband and carrier may be simultaneously impressed to detect the lowfrequency signaling currents represented by the side band, means toselect from the output of the detector theunmodulated carrier frequencycomponent, means to produce from the selected carrier component acurrent having characteristics depending upon the transmissionconditionsto which the carrier has been subjected, and means whereby a circuitelement of said receiving channel may be controlled in accordance withthe charactertistics of the current thus produced to compensate for thechange in efliciency of the transmitting medium.

10. In a system for controlling transmis sion, a transmitting mediumover which the carrier is transmitted together with the side band, thetransmission efliciency of said me dium being variable under differentconditions, a receiving channel including a detector upon which the sideband and carrier may be simultaneously impressed to detect the lowfrequency signaling currents represented by the side band, means toselect from the output of the detector the uninodulated carrierfrequency component, means to produce from the selected carriercomponent a direct current whose amplitude depends upon the transmissionconditions to which the carrier has been subjected, and means whereby acircuit element of' the receiving channel may be controlled inaccordance with the amplitude ot said direct current to compensate forthe change in efficiency of the transmitting medium.

11. In a system for controlling transmission, a transmitting medium overwhich the carrier is transmitted along with the side band, thetransmission efliciency of said medium being variable under differentconditions, a receiving channel including a detector upon which thecarrier and side band may be simultaneously impressed, means forselecting the carrier, means for producing from the carrier a currentwhose characteristics depend upon the transmission condi tions to whichthe carrier has been subjected, a circuit element in said receiving channel, and means for controlling said element in accordance with thecharactertistics of said current to compensate for the change inefiiciency of the transmitting medium.

12. In a system for controlling transmission, at transmitting mediumover which the carrier is transmitted along with the side band, thetransmission efficiency of said me dium being variable under differentconditions, a receiving channel upon which the carrier and side band maybe impressed, meansv for selectin the carrier, a rectifying device torectify tie selected carrier to produce a direct current having anamplitude depending upon the transmission conditions to which thecarrier has been subjected, a circuit element in said receiving channel,

and means for controlling said element in accordance with thea111plitude of the rectified current to compensate for the change inefficiency of the trans111itti11g medium.

l3. In a system for controlling transmission. 11 transmitting mediumover which the carrier is transmitted along with the side band, thetransmission eliicicncy of said me dium being variable under ditl'crentconditions, a receiving channel including a detector upon which thecarrier and side band may be impressed, means for selecting the carrier,means for producing from the selected carrier a current whosecharacteristics depend upon the transmission conditions to which thecarrier has been subjected, and means for controlling the efticiency ofsaid detector in accordance with the characteristics of the current thusproduced to compensate for the change in transmission efficiency of thetransmitting medium.

14. In a system for controlling transmission, a transmitting medium overWhich the carrier is transmitted along with the side band, thetransmission efticiency of said medium being variable under differentconditions, a receiving channel including a de tector upon which thecarrier and side band may be impressed, means for selecting the carrier,a rectifying device to rectify the selected carrier to produce a directcurrent having an amplitude depending upon the transmission conditionsto which the carrier has been subjected, and means to control theefliciency of said detector in accordance with the amplitude of therectified current to compensate for the change in efficiency of thetransmitting medium. I

15. In a system for controlling transmis sion, a transmitting mediumover which the carrier is transmitted together with the side band, thetransmission etficiency of said medium being variable under differentconditions, a receiving channel including a de tector upon which theside band may be impressed together with the carrier to detect the lowfrequency signaling currents represented by the side band, means toselect the unmodulated carrier component from the output of saiddetector, means to produce from said selected carrier component a directcurrent whose amplitude depends upon the transmission conditions towhichthe carrier has been subjected. and means to control the efficiency ofsaid detector in accordance With the amplitude of said direct current tocompensate for the change in transmission efiiciency of saidtransmitting medium.

16. In a system for controlling transmission, a transmitting medium overwhich the carrier is transmitted together with the side band, thetransmission efficiency of said medium being variable under differentconditions, a receiving channel including a detector upon which saidside band may be imdirect current to compen-" 17. The method ofcontrolling transmission in a carrier system in which the carrier istransmitted along with the side band and in which an amplifier isemployed at the receiving station, which consists in transmitting thecarrier and side band over a. medium Whose transmission is variableunderdifferent conditions, combining the carrier with the side band toproduce a low frequency signaling wave represented by the side band,selecting the unmodulated carrier, producing from the selected carrier acurrent having characteristics depending upon the transmissionconditions to which the carrier has been subjected, and controlling theefiiciency of the amplifier in accordance with the characteristics ofthe current thus produced to compensate for the change in efliciency ofthe. transmitting medium.

18. The method of controlling transmission in a carrier system in whichthe carrier is transmitted along with the side band and in which avacuum tube amplifier having a controlling grid is employed at thereceiving station, which consists in transmitting the carrier and sideband over a medium whose transmission is Variable under differentconditions, combining the carrier with the side band to produce lowfrequency signaling currents represented by the side band, selecting theunmodulated carrier component, rectifying the selected carrier componentto produce a direct current whose amplitude varies in accordance withthe transmission conditions to which the carrier has been subjected, andcontrolling the normal potential of the grid of the amplifier by saiddirect current to change its operating char acteristics to compensatefor the changes in the efficiency of the transmitting medium.

In a system for controlling transmis sion, a transmitting medium overwhich the carrier is transmitted together with the side band, thetransmission efficiency of said medium being variable under differentconditions, a receiving channel including an amplifier, means to combinethe side band with the carrier to produce low frequency signalingcurrents represented by the side band, means to select the'unmodulatedcarrier frequency component, means to produce from the selected carriercomponent a current having characteristics depending upon thetransmission conditions to which the carrier has been subjected andmeans whereby the efficiency of said amplifier may be controlled inaccordance with the characteristics of the currents thus produced tocompensate for the change in efiiciency of the transmitting medium.

20. In a system for controlling transmission, a transmitting medium overwhich the carrier is transmitted together with the side band, thetransmission efficiency of said me dium being variable under differentconditions, 3, receiving channel including a vacuum tube amplifier,means in said channel to combine the carrier with the side band toHERMAN A. AFFEL.

